Bisphenol A [2,2-bis(4-hydroxyphenyl)propane] is usually produced by reacting phenol with acetone in the presence of a homogeneous acid or a solid acid catalyst. The reaction mixture includes unreacted acetone, unreacted phenol, water and other by-products formed by the reaction, in addition to bisphenol A. The main component of the by-products is 2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl)propane (hereinafter, referred to as o,p′-BPA), and in addition, it includes trisphenol, a polyphenol compound, a chroman compound, colored impurities and the like.
Examples of a homogeneous acid to be used as a catalyst, include hydrochloric acid, sulfuric acid and the like. In the case where the homogeneous acid is used, since it is possible to proceed the reaction while precipitating crystals of an adduct of phenol with bisphenol A by reacting them at lower temperatures, bisphenol A can be produced with a high conversion of acetone and a high selectivity by decreasing the amount of the by-produced o,p′-BPA as an isomer thereof. However, the catalyst of the homogeneous acid such as hydrochloric acid requires a process for removing the catalyst from a reaction mixture or for neutralizing the catalyst, and thus the operation becomes complicated. Homogeneous dissolution of the acid in the reaction solution further causes corrosion of an apparatus or the like used in the reaction. Therefore, the reaction apparatus should use expensive and anti-corrosive materials, thus being uneconomical.
As a solid acid catalyst, a sulfonic acid-type cation-exchange resin is usually used. The reaction for producing bisphenol A essentially proceeds only with an acid catalyst, but if such a solid acid catalyst is used, the process in which acetone diffuses from the surface of the catalyst particles to an active site on the catalyst is involved, and thus the reaction rate is low. Thus, there is a general method used for improving the catalytic activity and the selectivity by allowing a compound containing a mercapto group to coexist in the reaction system (For example, JP-B Nos. 45-10337, 46-19953, etc.).
Further, it is proposed in JP-A No. 62-178532 to use a sulfonic acid-type cation-exchange resin in a fine particle or a fine powder having an effective diameter of 0.3 mm or less for obtaining a sufficient reaction conversion.
Various improvements on the structure of a resin product, which is the base material of a sulfonic acid-type cation-exchange resin, have been made. The sulfonic acid-type cation-exchange resin is a resin obtained by sulfonating a styrene-divinylbenzene copolymer which is obtained by radically copolymerizing styrene and divinylbenzene. The divinylbenzene in polymerization does not only prevent a polystyrene chain from dissolving in an organic solvent, but the content thereof is also an important factor in controlling the size of a pore, i.e., the size of a gel micropore within the sulfonic acid-type cation-exchange resin formed by capturing a polar solvent, or the mechanical strength of the sulfonic acid-type cation-exchange resin.
In other words, a sulfonic acid-type cation-exchange resin with a low content of divinylbenzene has a high catalytic activity due to a large gel micropore, but the mechanical strength is low. In addition, in the case where the content thereof is high, the mechanical strength increases, but the gel micropore size decreases, which causes decreased activity. JP-A Nos. 5-97741 and 6-320009 describe a method which complements the respective defects by simultaneous filling a sulfonic acid-type cation-exchange resin having a low content of divinylbenzene and a sulfonic acid-type cation-exchange resin having a high content of divinylbenzene into a reactor. Further, it is reported in WO 00/00454 that an improvement on a reaction conversion, which suggests a sulfonic acid-type cation-exchange resin having large gel micropores by using large molecules such as divinylbiphenyl instead of divinylbenzene.
The sulfonic acid-type cation-exchange resin in these methods described above comprises as a base material, atactic polystyrene which is obtained by radically copolymerizing styrene and a polyvinyl aromatic compound such as divinylbenzene. Since the atactic polystyrene is an amorphous resin without having a sharp melting point, a commercially available ion-exchange resin comprising the atactic polystyrene having a sulfone group introduced thereinto has room for improvement in heat resistance and is thus known to generate an effluent when it is used under the heating condition of 80° C. or higher. Thus, this causes problems such as deterioration in mechanical strength, decrease in the activity due to clogging of gel micropores, and deterioration over a prolonged period, and thereby there is an obstacle in using thereof at higher temperatures.
In order to overcome such problems, a method has been used which increases the degree of crosslinking and improves heat resistance in an atactic polymer chain. Since the diffusion within the ion-exchange resin particles is extremely lowered as the degree of crosslinking is increased, a large hole referred to as a “macropore” is formed within the particles by a physical treatment in order to improve the diffusion within the particles.
However, in the case where an ion-exchange resin having this macropore adsorbs a molecule having high polarity, such as water, a crosslinked structure tends to inhibit the bulge of particles caused by the swelling, which eventually collapses when it can no longer endure the swelling. Therefore, the development of a heat-resistant ion-exchange resin, which can be treated with an aqueous solvent, is demanded.
It is described in U.S. Pat. No. 3,342,755 that halogen is substituted for hydrogen on the tertiary carbon adjacent to the benzene ring of the styrene moiety in order to overcome the above described problem. However, the substitution of halogen for hydrogen leads to elution of chlorine from the resin, and thus a new problem occurs of incorporating halogen into a reaction mixture.
Further, as a highly heat-resistant ion-exchange resin, a perfluorosulfonic acid-based resin such as nafion is known, in which the maximum amount of acid is about 1.0 milliequivalent/g. Since this polymer skeleton is formed by copolymerization of tetrafluoroethylene and a trifluorovinyl alcohol derivative, an introduction exceeding a given amount of the trifluorovinyl alcohol derivative is problematic in terms of the polymerization technologies, which means that it is impossible to increase the amount of acid.
Further, it is described in the respective papers of Polymer Preprints, Vol. 34, p. 852 (1993), Macromolecules, Vol. 27, p. 287 (1994), Polymer International, Vol. 50, p. 421 (2001) or the like, a process for synthesizing a crystalline polymer containing a sulfone group, in which a sulfone group is introduced into syndiotactic polystyrene, and then crystallized. It is believed that it is necessary to remarkably suppress the amount of acidic functional groups to be introduced, in order to crystallize the sulfonated syndiotactic polystyrene later. Therefore, in this example, the maximum amount of acid is only 1.0 milliequivalent/g, thus being inadequate for a practical catalyst use.
As such, any ion-exchange resin product which has heat resistance and a high amount of acid, and can be used as a catalyst has not been exemplified. If an ion-exchange resin having heat resistance and a high amount of acid can be developed, the ion-exchange resin can be used as a solid catalyst at a high temperature in the reaction using a conventional ion-exchange resin at a low temperature or using a mineral acid as a catalyst, for example, the hydration of isobutene and propylene, the synthesis of bisphenol A from phenol and acetone, the synthesis of methylenedianiline from aniline and formaldehyde, and the like, thus it being an extremely useful catalyst in the industry.    [Patent Document 1] U.S. Pat. No. 3,342,755    [Patent Document 2] JP-A No. 2004-55165    [Non-Patent Document 1] Polymer Preprints, Vol. 34, p. 852 (1993)    [Non-Patent Document 2] Macromolecules, Vol. 27, p. 287 (1994)    [Non-Patent Document 3] Polymer International, Vol. 50, p. 421 (2001)